The intermodal transport of semi-trailers on ocean going barges and flatbed railcars is well known in the prior art. One known method of attaching or “tying down” semi-trailers for transport on railcars utilizes a collapsible stanchion having a “fifth wheel” mounted thereon which mimics the connection point on the rear of a typical on-road tractor. This apparatus operates as illustrated in FIGS. 1 through 3.
FIG. 1 shows stanchion 40 in a collapsed position about to be pulled erect. The erection is accomplished using an operable hook 12 pivotally mounted to the rear of a terminal tractor 10. Tractor 10 is positioned over stanchion 40 and hook 12 is pivoted down into engagement with an opening (not shown) defined in vertical strut 42 of stanchion 40. FIG. 1 shows hook 12 lowered and engaged in the opening.
In FIG. 2, stanchion 40 has been pulled partially erect by the forward motion of tractor 10. The four main parts of stanchion 40 are now exposed. Stanchion 40 is comprised of vertical strut 42, which will bear the weight of semi trailer 8 when erect; diagonal strut lower portion 46, which is fixed to railcar deck 18 by a pinned connection; a shorter diagonal strut upper portion 44, which is pivotally mounted to both vertical strut 42 and diagonal strut lower portion 46; and top plate 48, which will bear the weight of semi trailer 8 and lock onto the kingpin of trailer 8 to keep trailer 8 and railcar 18 together during travel over the railway.
FIG. 3 shows stanchion 40 in its fully erect position. Stanchion 40 is locked in this position by diagonal strut 45 formed by upper diagonal strut portion 44 and lower diagonal strut portion 46. When fully erect, the joint between upper diagonal strut portion 44 and lower diagonal strut portion 46 is locked against rotation and will remain locked until an abutting plate on terminal tractor 10 is backed against release trigger 14 shown in FIG. 3. Through suitable linkage, the backward motion of tractor 10 against release trigger 14 will unlatch the joint of diagonal strut 45, simultaneously releasing the kingpin and permitting the collapse of stanchion 40 back into the position of FIG. 1.
While the collapsible stanchion as illustrated in FIGS. 1-3 is operable, it suffers from a serious design flaw. To be locked into place, the upper and lower portions 46 and 44 respectively of diagonal strut 45 must be moved slightly beyond their straight line position as defined by the end fastening pins of the two portions 46 and 44, and the center pivot pin all having their centers in one straight line. The reason for this is that a hard stop of high strength is provided to prevent folding of the strut in the wrong direction. By latching the strut slightly over center (i.e., wherein the diagonal strut is beyond its straight line position), any longitudinal compressive force imparted to the diagonal strut by, for example, switching impacts to the car, or slack action when traveling in a train, will force the strut to fold slightly against its hard stop instead of placing the load on the latching mechanism, thereby freeing the latch mechanism from having to bear these very high forces.
Because no amount of statically applied pull on the ends of diagonal strut 45, even up to the breaking strength of diagonal strut 45 could cause this over center alignment to occur, the instructions usually given to operators simply advises that to lock diagonal strut 45 the motion of vertical strut 42 must be rapid enough that diagonal strut 45, because of inertia, will “snap”, that is, travel beyond the straight line condition, and lock into place at the over center position.
This is shown in FIG. 4. FIG. 4(a) shows strut 45 before upper portion 44 and lower portion 46 are situated in a straight line. Spring operated latch 50, mounted on upper portion 44, is just touching fixed catch 52, mounted on lower portion 46. FIG. 4(b) shows strut 45 closer to its straight-line position. Note that that the closer strut 45 gets to its straight line position, the lesser is the force exerted to move it further into its straight line position. For example, in the position shown in FIG. 4(b) a tension of 250# will only produce a force of about 23# operating to straighten the strut. FIG. 4(c) shows strut 45 in a completely straight position, but with latch 52 no yet engaged. Finally, FIG. 4(d) shows strut 45 moved past the straight position by approximately 3/16″ at 54. At this position, latch 52 is forced into position by springs 51 and stanchion 1 will remain safely erect.
Unfortunately the conditions under which the portion of diagonal strut 46 and 44 will lock into place are seldom, if ever, well defined, and no method exists for assuring the speed necessary to bring about the desired locked up condition. The variables affecting this operation (weather, temperature, cleanliness or lack thereof, lubrication, fit and condition of parts, initial manufacturing tolerances and wear, to name the most obvious) are so varied and variable that the perfect tractor speed on one day might fail the next. Regrettably, the drivers who must load trailers cannot know or control any of the variables except for tractor speed, and in trying to assure lockup of the stanchion, have a tendency to pull harder on stanchion 40 than may be necessary to bring about the locked condition. This can result in failure of the stanchion, and, if the car and the stanchion are made strong enough to resist the resulting forces, damage to the tractor can result. Therefore, it would be desirable to provide an improvement to this design in which the two portions of diagonal strut 45 become locked under conditions that are better defined, can be inspected in service and which do not require the “snapping” of the portions into place.
With the need for high speed pull-ups of the stanchion eliminated from the tractor operating protocol, a maximum speed during pull-up can be imposed (either by the driver or through some form of automatic control) and the hitch and tractor failures mentioned above can be reduced or eliminated.